This invention relates to lubricating agents for processing synthetic yarns (spin finish for synthetic yarns) and a method of processing synthetic textured yarns by using such lubricating agents, and more particularly to lubricating agents which exhibit significantly improved ability to prevent deposit on heaters used in the heating processes (hereinafter abbreviated as heater-deposit resistance) as well as lubricity, cohesion of yarn and anti-static capability.
In the field of production and manufacturing of thermoplastic synthetic fibers, there have recently been improvements in productivity due to semi-automation and shortening of processes. Production of partially oriented yarns (hereinafter abbreviated as POY) and successive or simultaneous draw-false twisting for the production of textured yarn are now being proposed. Faster execution of these processes is also attempted and this trend is presently growing at a fast rate.
With the acceleration in these processes, there arise new requirements for the lubricants to be used in such processes. Since the yarn speed increases and so does the contact pressure on the yarns which run against various machine parts such as rollers, guides, heaters for heat treatments and disks, the lubricating agent must provide high levels of lubricity, cohesion of yarn and anti-static properties to raw yarns for false twisting and in particular to those for drawing-false twisting. Moreover, when there is an increase in the amount of yarns that pass through a heater for heat treatment per unit time or in the torsional strain on the yarns, the centrifugal force will also increase and this will cause all kinds of materials to scatter around. Since the heaters for heat treatments must be made longer and their surface temperature must be raised in order to supply sufficient heat to the filaments for setting crimps, this tends to enhance the thermal degradation of the materials that fall off. Where such thermally degraded components (such as tar) are accumulated on the surface of these heaters, there arise such ill effects as fuzz, breakage of filements and spotty crimps. For this reason, lubricants are now required which are capable of preventing materials from falling off and are superior in heater-deposit resistance.
Lubricating agents containing various compounds have already been proposed for application in the spinning process for smooth execution of the subsequent false twisting process. As explained above, however, it is already impossible with the conventional lubricants to adequately satisfy the conditions for false twisting process which are becoming ever severer. What is actually being done is, for example, to stop the operation of apparatus now and then to clean the surfaces of the heaters. This not only causes a loss in thermal efficiency but also is a movement backwards away from automation because manpower must be expended for the cleaning work, resulting in reduction in production efficiency. Now that the speed of false twisting process is increasing rapidly, it is indispensable that a lubricant used for this process should satisfy the requirements regarding heater-deposit resistance, lubricity, cohesion of yarn and anti-static capability as a whole.
For improving the heat resistance of a feed yarn in heat treatment processes, it used to be considered important to improve the heat resistance of the lubricant itself and studies were made of various lubricants which would not themselves undergo thermal degradation to deposit on the heaters. Examples of such lubricants are shown below, but they are unsatisfactory for one reason or another.
Regarding lubricating agents which are the principal components of lubricating agents, mineral oils and esters of aliphatic acids are inferior from the points of view of fuming characteristics and generation of tar. Esters with quaternary carbon introduced into their molecules (Japanese Patent Tokukai Sho 50-53695) and esters of polyoxyalkylenated bisphenol and aliphatic acid (Japanese Patent Tokko Sho 53-43239) lack the ability to reduce generation of tar. Polydimethylsiloxane and its end modified products generate static electricity significantly and lack scouring ability and compatibility with other components of the lubricants (Japanese Patent Tokko Sho 58-12391, Tokukai Sho 55-67075). As for modified silicones such as methylphenyl polysiloxane and polyepoxysiloxane, they themselves generate insoluble, thermally degraded sludge on the surfaces of the heaters if too much of them (in excess of 10 weight %) is used as components of a lubricant (Japanese Patent Tokukai Sho 49-30621 and Tokukai Sho 51-67415). Even with polyether-type compounds which are considered to be the most useful lubricating agents among known compounds (Japanese Patent Tokukai Sho 56-31077), the problem of heater-deposit occurs as explained above under the severe changes in various conditions related to the increase in the rate of false twisting process. It has also been pointed out that the degree of deposit may increase even more, depending on the type and amount of emulsifier or anti-static agent added to them.
As for constituents other than lubricating agents, addition of a small amount of antioxidant can produce some favorable effects (Japanese Patent Tokko Sho 48-17517 and Tokukai Sho 53-19500) but it is not suitable under conditions of high-speed texturing process. Examples whereby a small amount of polydimethylsiloxane, methylphenyl polysiloxane or polyepoxysiloxane (less than about 10 weight %) is added do not show reduction in generation of tar (Japanese Patent Tokko Sho 54-5040 and Tokukai Sho 55-137273) and they are generally water-insoluble (even if a large amount is used). Moreover, since these compounds should be emulsified in water as components of the lubricant, the added emulsifier itself tends to become a source of heater deposit.
As for components other than lubricating agents such as polyalkylene oxide modified polysiloxane, polyethylene oxide modified polysiloxane does not have sufficient heater-deposit resistance as a lubricant for raw yarns for false twisting (Japanese Patent Tokko Sho 44-27518). As for the use of a polyether compound in combination with linear organic polysiloxane with kinetic viscosity in excess of 15 cst (Japanese Patent Tokukai Sho 48-53093), heater-deposit resistance has been found to be too small in the case, for example, of methyl(polyethylene oxide)polysiloxane. As for the use of a large amount (over 35 weight %) of polyalkylene oxide modified solicone in combination with polyalkylene oxide with affinity (Japanese Patent Tokukai Sho 50-59551), the idea is to reduce the amount of dropping from filaments of modified silicone onto the heaters so that improvement would be made regarding the generation of white sludge on heaters but since, as described above, an increased speed of false twisting or drawing-false twisting results in an increase in the centrifugal force on the yarn, it is extremely difficult to prevent by a physical means to prevent the lubricant constituents from becoming squeezed out and let fly off the fiber surfaces. As for the method of using polyalkylene oxide modified polysiloxane in combination with a reactive silicone compound in the ratio (former/latter) of 5 to 400/100 in weight (Japanese Patent Tokukai Sho 52-96297), the modified polysiloxane itself generates thermally degraded insoluble sludges on the heater surfaces if more than 10 weight % of it is used as component of the lubricant.